The present invention relates to electrophotography and, more particularly, to a method of maintaining the optimum conditions of an electrophotographically duplicated image, in which all the conditions of the duplicating or copying process are automatically changed to produce a correct duplicated image.
For the purpose of automatically correcting the variation from the initial conditions to set the optimum conditions of the duplicating process, it is hertofore a common practice for the duplicator to place a reference copy having a predetermined reflection factor on the contact glass section and detect the surface potential of a photosensitive medium corresponding to the above-mentioned reference copy thereby determining the bias potential at the developer section. Such a practice is very effective when the copy to be duplicated is of a uniform tone or, in other words, when the background of the copy is of one tone; however, when the copy has a colored background as in the case of a colored copy, it cannot necessarily produce a desirable duplicated image because the user must correct the exposure condition and so forth on the so-called sixth sense. In another conventional practice, the quantity of light reflected from the above-mentioned reference copy is detected and then the various conditions of the duplicating process are set according to the above-mentioned quantity of reflected light; this practice, however, can only correct the contamination condition of the optical system and still has the above-mentioned defects.